The present invention relates generally to ferrules for mounting upon the end portions of optical fibers and, more particularly, to angled physical contact (APC) ferrules and associated methods and apparatus for fabricating APC ferrules.
A variety of ferrules have been developed to facilitate the interconnection of optical fibers, with other optical fibers, optical devices or the like. For example, a number of standard ferrules, such as SC, FC, and ST ferrules, have been designed. Regardless of their type, ferrules typically define one or more longitudinal extending bores for receiving end portions of respective optical fibers.
One common type of ferrule is an APC ferrule that is designed to make physical conduct with another APC ferrule during the process of interconnecting a pair of optical fibers. Notably, the front face of an APC ferrule is disposed at a nonorthogonal angle, i.e., at other than 90xc2x0, relative to the longitudinal axis defined by the ferrule. For example, the front face of an APC ferrule is commonly disposed at an angle of approximately 8xc2x0 relative to a plane that extends perpendicular to the longitudinal axis defined by the ferrule. In order to interconnect a pair of APC ferrules, the ferrules are therefore positioned such that the angled front faces are complimentary to one another, that is, the forwardmost portion of the front face of one ferrule is preferably aligned with the rearwardmost portion of the front face of the other ferrule and vice versa. In order to facilitate the alignment of the ferrules in this complimentary fashion, the ferrules typically include a key that is disposed in a predetermined relationship to the front face of the ferrule. Thus, a connector sleeve or the like can be utilized to engage the keys of a pair of APC ferrules to insure that the ferrules are mated in a complementary fashion.
The angled front face of an APC ferrule advantageously reduces undesirable reflections of optical signals at the interface between a pair of optical fibers, thereby decreasing optical power losses and correspondingly increasing optical power transmission. In addition to forming the ferrule to have a front face that is disposed at a predetermined angle relative to the longitudinal axis defined by the ferrule, the front face of some APC ferrules has a spherical shape. In this regard, if an APC ferrule is constructed such that the apex of the spherical surface substantially coincides with the bore defined by the ferrule, physical contact between the end portions of the respective optical fibers is facilitated, thereby enhancing optical transmission between the optical fibers. Unfortunately, it is relatively difficult to shape the spherical surface of an APC ferrule such that the apex of the spherical surface coincides with the bore defined by the ferrule. Instead, APC ferrules having a spherical front face generally have an apex offset that is defined as the distance by which the apex of the spherical surface is offset from the bore defined by the ferrule. While some apex offset can be tolerated while still maintaining optical transmission between the respective optical fibers, signal transmission can be adversely impacted if the apex offset becomes too large, such as greater than 50 microns. The degree of apex offset that can be tolerated is dependent upon several factors including whether the optical fibers are single mode or multimode, as well as the radius of curvature of the spherical surface. In this regard, greater apex offsets are typically acceptable for spherical surfaces having larger radii of curvature than for spherical surfaces having smaller radii of curvature.
Conventional APC ferrules that are to include a spherical front face typically require that the amount of material that is removed from the front face of the ferrule to define the spherical surface be precisely controlled so as to form the spherical surface in such a manner that the apex of the spherical surface coincides with the bore defined by the ferrule. In this regard, the removal of either too much or too little material during the process of grinding the front face of an APC ferrule into a spherical shape would typically result in the apex of the spherical surface being offset from the bore defined by the ferrule. In an attempt to minimize the apex effect, at least some of the prior techniques for grinding the front face of an APC ferrule to define the spherical surface are relatively complex, thereby decreasing the efficiency and increasing the cost at which APC ferrules can be fabricated.
One exemplary APC ferrule is described by U.S. Pat. No. 5,351,327 along with several techniques for fabricating the APC ferrule. As described, the APC ferrule has a spherically shaped front face with an apex offset of no more than 50 microns and, more typically, no more than 10 microns. While several different fabrication techniques are described, most of the techniques require that the front face of the ferrule be formed into a temporary surface that is then repolished to form the desired spherical surface. The temporary surface can be either flat or spherical and is typically angled or inclined relative to a plane perpendicular to the longitudinal axis defined by the ferrule. Unfortunately, the repolishing of the front face and the other finishing operations disadvantageously consume polishing consumables and reduce the efficiency with which the ferrules can be fabricated.
In addition, U.S. Pat. No. 5,148,660 describes an APC ferrule having a spherical front surface that is angled relative to a plane perpendicular to the longitudinal axis defined by the ferrule. The APC ferrule described by U.S. Pat. No. 5,140,660 includes a cylindrical tip or pedestal that extends forwardly from the main portion of the ferrule body and that has a smaller diameter than the main portion of the ferrule body. As such, the cylindrical tip may damage surfaces that come into contact with the front face of the ferrule, such as by tearing polishing film or cleaning clothes.
While a number of APC ferrules have therefore been proposed that include spherical front faces, each of these conventional APC ferrules is subject to some shortcomings. For example, the process of grinding the front face of the ferrule may have to be closely monitored since the removal of too much or too little material may disadvantageously increase the apex offset. In addition, some APC ferrules may require extensive polishing or other finishing operations such that the front face is sufficiently smooth, thereby increasing the fabrication costs and the resulting cost of the APC ferrules. Thus, with increasing emphasis being placed upon lowering the cost of ferrules and reducing the permissible tolerances of the ferrules, an improved APC ferrule is desired that offers a reduced apex offset and that can be fabricated in a relatively simple fashion, thereby reducing fabrication costs and the cost of the resulting APC ferrules relative to conventional fabrication techniques.
A ferrule is therefore provided that can be fabricated in a repeatable and an efficient manner so as to have a relatively small apex offset. In this regard, a method and apparatus for fabricating a ferrule are also provided that grind a portion of the front face of the ferrule into a hemispherical shape with a relatively small apex offset regardless of the amount of material that is removed from the front face of the ferrule. Since the apex offset is not dependent upon the amount of material removed from the front face of the ferrule to define the hemispherical surface, the method and apparatus for fabricating the ferrule can be performed in a repeatable manner with a minimum number of finishing steps being required after the grinding process to complete the fabrication of the ferrule.
According to one advantageous aspect of the present invention, a ferrule is provided that includes a ferrule body extending lengthwise between opposed front and rear faces and defining a longitudinal axis. The ferrule body also defines a lengthwise extending bore capable of receiving an end portion of an optical fiber. According to the present invention, the front face of the ferrule body includes a plateau defining a plane that extends perpendicular to the longitudinal axis and a hemispherical portion through which the bore opens. Typically, the hemispherical portion is rearward of the plateau such that the plateau defines the forwardmost portion of the ferrule body.
The hemispherical portion of the front face of the ferrule body is preferably angled relative to the plateau and to the plane perpendicular to the longitudinal axis defined by the plateau. In this regard, a plane tangent to the hemispherical portion at a point coincident with the longitudinal axis is disposed at an offset angle, typically between 8xc2x0 and 12xc2x0, relative to the plane perpendicular to the longitudinal axis such that the resulting ferrule is an APC ferrule. The plateau is generally smaller than the hemispherical portion with the plateau typically extending across less than 50% of the front face of the ferrule body, and the hemispherical portion extending across more than 50% of the front face of the ferrule body. The plateau is also typically disposed proximate a side surface of the ferrule body and, in instances in which a portion of the ferrule body proximate the front face is chamfered, the plateau is preferably disposed proximate the chamfer.
By constructing the ferrule to have a front face that includes a plateau and a hemispherical portion, the ferrule of the present invention provides an angled front face for minimizing reflections and for facilitating optical coupling with the optical fiber upon which the ferrule is mounted. In addition, the ferrule of the present invention can be readily fabricated such that the apex offset that is both repeatable and relatively small.
According to another aspect of the present invention, a method and apparatus for fabricating a ferrule, such as an APC ferrule, are provided. In this regard, the ferrule is initially secured within a mounting fixture, such as a collet, such that the front face of the ferrule is exposed. At this initial stage of the fabrication process, the front face of the ferrule is typically perpendicular to the longitudinal axis defined by the ferrule. A grinder is also provided that includes a spindle adapted for rotation about a spindle axis that is offset by a predetermined angle, such as between 8xc2x0 and 12xc2x0, from a plane perpendicular to the longitudinal axis. The grinder also includes a grinding wheel mounted upon the spindle for rotation therewith about the spindle axis. To impact the spherical surface, the grinding wheel has an arcuate grinding surface that generally defines a radius of curvature of between 5 mm and 12 mm. The grinder is also adapted to rotate both the spindle and the grinding wheel about an offset axis that is orthogonal to the spindle axis and is coplanar with both the spindle axis and the longitudinal axis defined by the ferrule. Typically, the grinder rotates the spindle and the grinding wheel at a faster rate about the spindle axis than about the offset axis.
At least one of the grinding wheel and the ferrule is then advanced toward the other by means of a translation device such as a translation stage. In particular, the translation device advances at least one of the grinder and the mounting fixture toward the other along a motion axis that extends parallel to the longitudinal axis and that is coplanar with the spindle axis, the offset axis, and the longitudinal axis. During this advancement, the grinding wheel is rotated about both the spindle axis and the offset axis in order to engage and grind a portion of the front face of the ferrule into a hemispherical shape. Typically, the advancement of at least one of the grinder and the mounting fixture is halted prior to grinding all of the front face of the ferrule into a hemispherical shape such that a portion of the front face of the ferrule remains as a plateau that extends substantially perpendicular to the longitudinal axis defined by the ferrule.
While either or both of the grinder and the mounting fixture can be advanced toward the other, a translation stage typically advances the grinder toward the ferrule along the motion axis, while the mounting fixture remains fixed in position. In order to insure that the proper portion of the front face of the ferrule is ground into a hemispherical shape, the position of at least one of the ferrule and the grinder is adjusted relative to the other before commencing grinding. In this regard, the apparatus can include a plurality of adjustment stages for adjusting the position of the mounting fixture in respective planes relative to the grinder.
By fabricating the ferrule according to the method and apparatus of the present invention, a ferrule having an at least partially angled front face and a relatively small apex offset, such as 50 microns or less, can be fabricated in a repeatable and an efficient manner. In this regard, since the front face of the ferrule has both a plateau and a hemispherical portion, the apex offset is not dependent upon the amount of material removed from the front face during the process of grinding the hemispherical surface. As such, ferrules can be repeatedly fabricated that have approximately the same relatively small apex offset. In addition, the method and apparatus for fabricating the ferrule of the present invention also minimizes finishing steps that would otherwise have to be taken in order to complete the fabrication of the ferrule, such as by minimizing the subsequent polishing of the front face of the ferrule since the grinding procedure also produces a relatively hemispherical surface. Thus, the efficiency of the fabrication process is increased and the costs of fabrication are potentially decreased.